High-performance thermoplastic polyimide enabled by ketone-based diamine monomer

Thermoplastic polyimide (TPI) as adhesive can meet the requirements of flexible copper clad laminates (FCCLs) applied under extreme condition. Incorporating flexible groups, asymmetric structures and bulky side groups into the main chain, and copolymerization are common ways to achieve thermoplasticity, through reducing the rigidity of polymer chains or intermolecular interaction. However, it induces a trade-off between thermoplasticity and thermal dimensional stability as well as mechanical property. Furthermore, the adhesion strength between TPI film and copper foil is highly desirable in FCCL. Herein, we develop a ketone-based diamine 1,3-phenylenebis((3′-amino-[1,1′-biphenyl]-4-yl)methanone) (Ph-BiAmMe) to afford copolymerized TPI with 4,4′-oxydianiline (ODA) and 3,3′,4,4’-Biphenyltetracarboxylic dianhydride (BPDA). As for thermoplasticity, flexible linkages such as ether and ketone enhance the movability of polymer chains, and copolymerization weakens the intermolecular interaction between polymer chains to some extent. Furthermore, the incorporation of Ph-BiAmMe promotes denser chain packing and stronger CTC effect, thereby maintaining good thermal dimensional stability and mechanical properties. Simultaneously, ketone moieties enhance the peel strength of TPI when bonded with copper. Based on this strategy, the as-prepared TPI shows good thermoplasticity with a proper T_g of 274 °C. Meanwhile, it preserves a low CTE of 46.5 ppm K⁻¹, high tensile strength of 117.4 MPa, elongation at break of 27.3 % and peel strength of 1.11 N mm⁻¹.